Magnetic disc cartridge with ventilating structure

ABSTRACT

A magnetic disc in a cartridge is ventilated to keep a data containing surface portion thereof substantially free of particulate materials. A recirculating gas path includes apertured conduits for supplying gas jets completely across the portion as the disc is rotating in an enclosure. An orifice removes gas from the enclosure. A fan circulates the gas removed from the enclosure through the orifice and supplies the circulated gas back to the apertured conduits. Magnetic heads are positioned relative to the orifice and an inlet for the gas jets such that the gas has laminar flow as the gas passes the magnetic heads so the gas flow does not affect the position of the heads relative to the disc portion. The recirculating path includes filters for removing particulate materials from the recirculating gas.

TECHNICAL FIELD

The present invention relates generally to magnetic disc memories and more particularly to a magnetic disc memory method and apparatus wherein gas is circulated across the disc to keep a disc face free of particulate material and to a cartridge particularly adapted to be used with such a memory.

BACKGROUND ART

Magnetic disc memory units are widely used in data processing systems because such units have high storage capacity and require relatively short time for read/write heads of a disc memory to access data stored at a given point on the disc in response to a disc memory address supplied to the memory unit. Magnetic discs employed in disc memory units carry data on circular concentric tracks, typically positioned on both sides of the disc. The tracks generally have a width of no more than a few dozen microns. To transduce, i.e., read and write, data on the disc, magnetic heads of the memory units are positioned adjacent opposite faces of the disc, at a distance of a few tenths of a micron.

The magnetic discs are rotatably driven by an electric motor of the disc memory unit at a constant rotational speed. Current memory units frequently include a limited number of discs, i.e., one or two discs, and have a relatively limited storage capacity, on the order of ten to several tens of millions of bytes. Each byte typically includes eight bits, i.e., a binary digit data unit having a value equal to one or zero, as indicated by a magnetic flux transition on a track of the disc. Typically, at least one disc is enclosed in a cartridge that is selectively inserted into and removed from a receptacle of the magnetic disc memory unit. A disc memory unit receptacle normally contains only a single removable cartridge. When a cartridge is immediately inserted into the receptacle as soon as read and/or write operations have been completed on the disc in the initially inserted cartridge. Thus, plural removable cartridges, each containing at least one magnetic disc, are used with a single disc memory unit.

Certain disc memory units contain two magnetic discs, one of which remains permanently inside the disc memory unit; the other disc is contained in a cartridge that is selectively inserted and removed from the disc memory unit receptacle.

Cartridges containing removable magnetic discs have standarized shapes and dimensions, enabling them to be used interchangeably with magnetic disc units of different manufacturers. Thereby, the standarized cartridges are easily inserted into and removed from the receptacles of many different magnetic disc memory units. The cartridges are constructed to protect discs located therein from contamination by dust and other particulate matter during periods while the cartridges are not in use, i.e., while a particular cartridge is not in a magnetic disc memory unit receptacle. The prior art cartridges typically include structure for ventilating the disc while the cartridge is in the disc memory unit receptacle, thereby to insure that the disc remains extremely clean, to increase reliability of data read from the disc. Exemplary of such a cartridge which is selectively inserted into and removed from a receptacle of a magnetic disc memory unit is disclosed in U.S. Pat. No. 4,078,246, commonly owned with the present invention, and entitled "Container For A Magnetic Disc".

The cartridge disclosed in the U.S. Pat. No. 4,078,246 contains a rigid disc having a relatively small diameter. The cartridge is relatively flat, having a height less than one tenth the length or width thereof. The cartridge is inserted into a suitable disc memory unit receptacle. The cartridge includes a side wall having an opening which is normally closed while the cartridge is not in use, i.e., when the cartridge is not in the disc memory unit receptacle. When the cartridge is in the disc memory unit receptacle, magnetic read/write heads of the unit extend through the opening and are moveable relative to recording tracks on the disc. The cartridge includes a mechanism for coupling a hub carrying the disc to a rotary drive mechanism, usually an electric motor, of the disc memory unit.

The cartridge includes rigid, elastically deformable, opposed, generally parallel walls having a tendency to be outwardly convex in a free state. At the center of one of the parallel walls is an internal projection, forming an annular bearing surface facing an inside face of the one wall. The other wall includes an opening coaxial with the center of the one wall. The opening in the other wall is surrounded by an annular bearing surface on the outside face of the other wall. The disc is carried by an annular hub having internal and external flanges positioned to engage the bearing surfaces of the other wall. The axial spacing between the flanges is less than the spacing between the bearing surfaces of the other wall while the other wall is in the free state, whereby when the disc is in an idle state and the parallel walls are flattened an elastic restoring force mechanically holds the disc in proper position. When the cartridge is in the receptacle of the magnetic disc memory and the disc is being driven, the disc is able to turn because the walls are urged toward each other, with a concave configuration. The bearing surfaces and flanges are constructed so that the cartridge is sealed when not in use, thereby protecting the hub carrying the disc and the disc from dust particles. By selecting suitable relative positions and diameters for the flanges, the disc is automatically ventilated during operation in response to a centrifugal effect of air on opposite faces of the disc, to provide cleaning of dust and other particular matter from the disc surface, as well as cooling.

Other removable magnetic disc cartridges having different ventilating systems are known. Such a cartridge is disclosed, for example, in U.S. Pat. No. 3,812,534, entitled "Ventilation Device For Magnetic Disc Unit", and commonly owned with the present application.

A magnetic disc memory unit includes a receptacle for receiving the cartridge. The cartridge disclosed in U.S. Pat. No. 3,812,534 contains at least one magnetic disc and includes first and second lateral openings through which brushes and read/write heads are respectively introduced through walls of the receptacle.

The cartridge of U.S. Pat. No. 3,812,534 includes a conduit for receiving filtered air supplied to the receptacle through an opening in the cartridge. The air supplied to the cartridge leaves the cartridge through the opening in the cartridge through which the heads extend. The filtered air introduced into the cartridge is circulated with the turning disc in response to a centrifugal force produced by the disc rotation. The filtered air has a tendency to escape to the periphery of the disc in response to the centrifugal force. A regulator positioned in a filtered conduit for supplying air to the cartridge provides a constant air flow to the cartridge, which flow is relatively independent of pressure applied to a ventilation conduit intake, to prevent overly rapid clogging of the filter. Thereby, the life of the filter is prolonged, an advantageous feature because disc memories must normally be provided with very high capacity, relatively expensive air filters.

As disclosed, for example, in commonly owned U.S. Pat. No. 4,298,898 data written onto discs enclosed in removable cartridges are separated into adjacent, circular, equal sized segments, with each side or face of the disc being normally divided into several dozen segments. Each segment is divided into two portions of different sizes, such that the larger portion contains data processed or to be processed by a data processing system including the disc memory unit containing the cartridge. The smaller portion contains track identification data used by the data processing system for positioning the read/write magnetic heads of the memory unit relative to the disc tracks. Within each segment, the smaller portion is separated into a number of reference areas. The number of reference areas is equal to the number of tracks, such that each track is associated with a single, separate area. The number of data bits per unit length along the circumference of a disc track is referred to as "longitudinal data density", while "radial density" indicates the number of tracks per unit length measured along the disc diameter.

The current trend in developing magnetic discs is focused particularly on obtaining substantial increases in radial and longitudinal densities. Typically, radial densities are on the order of 350 to 400 tracks per centimeter, i.e., 850 to 1,000 tracks per inch (TPI), while the longitudinal densities are on the order of 2,000 bits per centimeter, i.e., 5,000 bits per inch (bpi).

It is difficult to obtain the same longitudinal and radial densities on removable magnetic discs enclosed in cartridges as on a disc which remains fixed permanently inside a disc memory unit. The removable feature of such cartridge enclosed magnetic discs is a limiting factor on the longitudinal and radial densities thereof because it is very difficult to obtain an adequately clean environment inside of the cartridge. Any cartridge that can not be air tight to the same degree as a disc which remains fixed permanently inside a disc memory unit may, due to variations in prevailing climatic conditions, absorb dust or other foreign particulate materials in varying quantities. Because the cartridge enclosure is separate from the enclosure in which magnetic read/write heads are situated when the cartridge is not inserted in a receptacle of the magnetic disc unit, there is a high probability that a certain amount of contaminated air enters the cartridge when the cartridge is inserted into the receptacle. In other words, air containing foreign particles originating from the disc memory unit enclosure containing the magnetic read/write heads has a tendency to enter the cartridge. Because foreign particulate materials, such as dust, may be as large or larger than the distance separating the magnetic heads and the magnetic coating on the disc, there is a high probability of errors occurring in reading or writing data.

Thereby, to obtain signals having the same spatial resolution as the resolution of magnetic variations on the disc it is necessary to minimize dust and other foreign particulate materials within the cartridge. In addition, it is necessary to eliminate residual dust which may remain in the cartridge after it has been inserted into the disc memory unit receptacle. Reducing contamination from dust and other foreign paticulate materials in the cartridge is difficult to achieve to an adequate degree in self ventilated cartridges, such as described in U.S. Pat. No. 4,078,246 because there frequently remains very minute particles on the disc surface, which particles have dimensions on the order of the space occupied by data bit on the disc.

It has also been found that a ventilation system such as described in U.S. Pat. No. 3,812,534 does not provide an adequate degree of cleanliness inside of the cartridge. In addition, the system disclosed in U.S. Pat. No. 3,812,534 exhausts air through the same opening as through which read/write heads are introduced; the air introduced through the same opening as the opening through which the read/write heads are introduced may disturb the position of the heads relative to the magnetic disc.

It is, accordingly, an object of the present invention to provide a new and improved ventilation system and method for a cartridge containing a removable magnetic disc, wherein contamination by dust or other foreign particles is considerably reduced.

Another object is to provide a new and improved magnetic disc cartridge having provisions for circulating gas against surfaces of the disc to dislodge particulate materials that adhere to the disc while in storage and prevent accumulation of such materials on the disc while in use.

DISCLOSURE OF INVENTION

In accordance with one aspect of the invention, an apparatus for ventilating a magnetic disc, to keep a surface portion of the disc containing data substantially free of particulate materials, includes means for recirculating gas over the disc, mounted in an enclosure for rotation about an axis. A recirculating gas path includes aperture means for supplying gas jets completely across the disc data containing portion as the disc is rotating. The gas jets remove particles that tend to adhere to the disc during storage and prevent particulate material from adhering to the disc portion while a cartridge containing the disc is in a receptacle of the memory unit. The path also includes an orifice for removing gas from the enclosure and fan means for circulating the gas removed from the enclosure by the orifice. The fan means circulates the gas about the axis as the disc is rotating and supplies the circulated gas back to the aperture means. The fan means accelerates air withdrawn from the enclosure through the orifice so that the gas has sufficient velocity to lift dust particles from the disc and prevent further dust particles from adhering to the disc while it is in the receptacle.

The recirculating path includes filter means for removing particulate materials from the gas circulating in the recirculating path between the orifice and the aperture means. The filter means includes separate first and second filters in an inlet and an outlet of the fan means. Preferably, the fan means is mounted coaxially with the disc in a chamber removed from the enclosure, so that the disc and fan means are in separate planes. The chamber containing the fan means is connected in fluid flow relationship with the enclosure only by the aperture means and the orifice.

To prevent particulate material contamination of the interior of the enclosure while the cartridge is not in place in the receptacle, a first gate means is positioned between an outlet of the fan means and the aperture means, while a second gate means is positioned between an inlet of the fan means and the orifice. In addition, an aperture in the enclosure through which read/write heads of the memory unit extend is closed simultaneously with closure of the first and second gate means while the cartridge is not in place in the receptacle.

To prevent movement of the head means by the gas which prevents particles from adhering to the disc, the aperture means and orifice are positioned so there is laminar flow across the head. In particular, the aperture means is disposed at different radii across the disc data containing portion while the orifice is positioned farther from the axis than any part of the aperture means. The aperture means and orifice are positioned so that the gas flows between them in an outwardly directed spiral through at least one complete revolution. Laminar flow past the head occurs because the head is more than a half revolution from the aperture means and orifice, as well as because side walls of the enclosure are smooth. Turbulence in the gas flow is minimized because the flow of gas in the spiral is in the same direction as the direction that the disc turns.

In accordance with another aspect, the invention is directed to a magnetic disc cartridge including first conduit means for supplying gas to the disc containing data portion to remove particulate material from the portion and prevent particulate material from adhering to the disc as the disc rotates about the axis. Second conduit means withdraws the gas supplied to the enclosure by the supply from the enclosure. The gas supply means and gas withdrawing means are part of a recirculating path for the gas. One of the conduit means includes a filter for removing particulate material from the gas. The enclosure includes an opening through which extend magnetic transducing head means of a disc memory unit when the cartridge is in place in a receptacle of the unit. Gate means close both the conduit means and the opening when the cartridge is in place in the receptacle.

It is, accordingly, still another object of the invention to provide a new and improved method of and apparatus for circulating gas in a magnetic disc enclosure, wherein the gas is circulated in such a manner as to prevent movement of magnetic head means of a memory unit with which the disc in the enclosure functions.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1, 2 and 3 are illustrations of an embodiment of a conventional, prior art cartridge containing at least one removable magnetic disc;

FIG. 4 is a three-quarters perspective view of the overall exterior outline of a cartridge ventilated according to the present invention, in combination with a disc memory unit frame and receptacle into which the cartridge is inserted;

FIGS. 5 and 6 are cross-sectional views of cartridges respectively containing one and four discs, which cartridges are assumed to be in an idle state, outside of the memory unit receptacle;

FIG. 7 is a cross-sectional view of the cartridge illustrated in FIG. 5, in the memory unit receptacle;

FIG. 8 is a three-quarters perspective view, in schematic form, of a ventilation system for the cartridge illustrated in FIGS. 5 and 7;

FIG. 9 is a top sectional view of a cartridge in accordance with the invention, in combination with a ventilation system in accordance with the invention, wherein the cartridge is illustrated as being positioned inside of a disc memory unit receptacle;

FIG. 10 is a three-quarters perspective view of a shell of a cartridge ventilated by a system according to the invention, wherein it is indicated how filtered air circulates inside of the cartridge;

FIG. 11 is a top sectional view of a cartridge in accordance with the invention when the cartridge is not inserted into the memory disc unit receptacle;

FIG. 12 is a side sectional view of one embodiment of a ventilation system in accordance with the invention, in combination with a single disc cartridge in accordance with the invention;

FIG. 13 is a top cross-sectional view of rotary fan mechanism that is part of the ventilation system in accordance with the invention; and

FIG. 14 is a cross-sectional view of a ventilation system in accordance with the invention, in combination with a four disc cartridge.

DETAILED DESCRIPTION OF FIGS. 1-3

To provide a better understanding of the principles of assembly and operation of the cartridge carrying removable magnetic disc according to the present invention, the prior art configuration illustrated in FIGS. 1-3 is considered. The cartridge illustrated in FIGS. 1-3 is of the type disclosed and illustrated in U.S. Pat. No. 4,078,246.

As illustrated in FIG. 1, magnetic disc 20 is enclosed in cartridge 10, configured as a relatively flat box having square top and bottom walls 11 and 12. One side wall 13 of cartridge 10 includes aperture 14, normally closed by shutter 15 when the cartridge is not being used, i.e., when the cartridge is not in a disc memory unit receptacle. Shutter 15 is operated by a known tamper proof internal mechanism, to insure that the aperture is not obstructed while the cartridge is in the magnetic disc memory unit receptacle. Immediately after shutter 15 is opened, magnetic read/write heads E/L, represented by an arrow in FIG. 1, are introduced into cartridge 10 to read data stored on both sides of magnetic disc 20. Cartridge 10 is formed by an assembly of parts made of a rigid, but elastically deformable material.

In FIG. 2, cartridge 10 is illustrated as being in an idle or rest state, outside of a magnetic disc memory unit, between successive operating periods. In FIG. 2, upper wall 11 is illustrated as including a center, internal projection 17, terminating with an external extractor ring flange 18, forming an annular bearing surface generally parallel to walls 11 and 12 within cartridge 10. Wall 12 includes an opening coaxial with projection 17. The edge of the opening in wall 12 is defined by annular bearing surface 19.

Disc 20 is a flat annular body 21 having flat parallel faces 22 and 23, both covered with a magnetic recording coating. Disc 20 includes annular hub 24 having axially spaced and opposed extremities in the interior and exterior of the volume between walls 11-13. The extremity of hub 24 within walls 11-13 carries an inwardly extending flange 25 that engages the top face of flange 18. The external extremity of hub 24 includes outwardly extending flange 26, having a top surface which engages the bottom face of flange 19 surrounding the opening in wall 12. Hub 24 includes an internal axial passage fitted with diaphragm, 27, which is either star shaped or perforated to enable gas to pass through it. Diaphragm 27 carries centering ring 28 having a frustoconical socket or tapered hole 29.

Opposing end walls 11 and 12 of cartridge 10 are maintained substantially planar and parallel to each other, as shown by the solid lines in FIG. 2 while the cartridge is at rest, i.e., not in use. The elastic nature of walls 11 and 12, however, tends to cause the walls to be flexed outwardly, to assume a convex shape, as shown by the dotted lines in FIG. 2. There is therefore an elastic restoring force exerted on walls 11 and 12 to maintain disc 20 in place while the cartridge is in an idle or storage period. Thereby, an air tight seal is provided where flanges 25 and 26 meet bearing surfaces 18 and 19.

In FIG. 3 the position of disc 20 inside of cartridge 10 is illustrated, assuming that the cartridge is in situ within a receptacle of a magnetic disc memory unit. In response to cartridge 10 being loaded into the receptacle, walls 11 and 12 are deflected into a concave condition so that the walls move closer to each other, as indicated by the solid line positions of walls 11 and 12. The relative movement of walls 11 and 12 between the rest and service conditions is indicated in FIG. 3 by comparing the dotted line positions of the walls, as subsists when the cartridge is not in use, and the solid line positions. Because walls 11 and 12 are deflected inwardly when cartridge 10 is in the receptacle, flanges 25 and 26 of hub 20 are disengaged from bearing surfaces 18 and 19 of cartridge 10 to enable the disc to be rotated, cleaned and ventilated while it is driven by motor assembly 20 of the disc memory unit. Disc 20 and hub 24 which carries it are driven by a motor, preferably an electric motor, of the disc memory unit. The motor is coupled to spindle 31 having a tapered head which fits into tapered hole 29 of centering ring 28. Fixedly mounted on spindle 31 is platter 32, having a longitudinally extending flange with an edge for engaging the bottom face of flange 26 of hub 24. Platter 32 is perforated and magnetically coupled between hub 24 and spindle 31.

In this conventional, prior art cartridge, dust and foreign particles are removed by a self ventilation process that occurs within the disc. In particular, natural ventilation is obtained by a centrifugal effect of air being rotated in response to the disc rotating. It can be shown that when very high radial and longitudinal densities are desired, the natural ventilation is inadequate to achieve complete decontamination of the disc, as well as the cartridge interior. It has been found that particulate materials, such as dust and other foreign particles, remain in the cartridge and on the disc. The dimensions of the particulate material are on the same order of magnitude as the spacing between the magnetic read/write heads and the disc surface, as well as on the same order of magnitude as the dimensions of the magnetic data variations recorded on the disc. Such foreign particles are therefore detrimental to the reliability of data read from the disc and can cause errors in reading track address in signals from the disc. Errors in reading track address signals result in positioning errors of the magnetic heads over the disc tracks. It has been found that the resulting magnetic head positioning errors can not be fully corrected by devices for controlling the position of the read/write heads over the disc tracks. It has also been found that a ventilation system, such as disclosed and claimed in U.S. Pat. No. 3,812,534 does not eliminate dust and other foreign particles sufficiently.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The cartridge of the present invention obviates the foregoing disadvantages in the prior art cartridges.

As illustrated in FIG. 4, cartridge CART₁, containing a single removable disc DISC₁, is designed to be inserted into receptacle 201 of frame BAT₁, a part of magnetic disc memory unit MEMO. Cartridge CART₁ includes grip PPR to facilitate handling by an operator who inserts the cartridge into receptacle 201. Cartridge CART₁ includes parallel, opposite side walls 202 and 203 in which are formed grooves RAIN₁ and RAIN₂. Grooves RAIN₁ and RAIN₂ are received in tracks RL₁ and RL₂ on opposite interior side walls of frame BAT₁ within receptable 201. Longitudinal tracks RL₁ and RL₂ enable cartridge CART₁ to be slid into receptacle 201 in the direction indicated by arrow FI.

Cartridge CART₁ includes an arcuate side wall 205 which generally extends between side walls 202 and 203. Side wall 205 includes aperture FE_(c), normally covered when cartridge CART₁ is out of receptacle 201, by a suitable shutter. In response to cartridge CART₁ being inserted into receptacle 201, the shutter covering aperture FE_(c) is opened to enable read/write heads TEL₁ and TEL₂ of memory MEMO to be inserted adjacent opposite faces of disc DISC₁. When cartridge CART₁ is not in receptacle 201, heads TEL₁ and TEL₂ are positioned behind a door normally closing aperture FE_(m) in side wall 206 in the receptacle, which side wall corresponds with side wall 205 of the cartridge.

As illustrated in FIG. 4, for example, a rotary drive mechanism for disc DISC₁ in cartridge CART₁ includes drive platter PLENM₁, an integral part of a spindle of an electric motor (not shown) of memory unit MEMO. Drive platter PLENM₁ includes a horizontal reference plane π (FIG. 7) for receiving hub MOY₁ (FIG. 5) of cartridge CART₁ when the cartridge is inserted in receptacle 201. Extending at right angles to plane π is the axis of rotation Ax_(r) of drive platter PLENM₁. Concentric with axis Ax_(r) and extending from plane π are circular flanges A₁ and A₂, having interior walls extending in a direction parallel to axis Ax_(r). Flange A₁ is at the outer periphery of platter PLENM₁, while flange A₂ is at an intermediate position between axis Ax_(r) and flange A₁.

As described infra in connection with FIGS. 7 and 12, memory unit MEMO includes a magnetic disc which remains permanently in frame BAT₁ ; to simplify FIG. 4, the magnetic disc located permanently inside of frame BAT₁ is not shown. Disc DISC₁ and the disc permanently located in frame BAT₁ are driven by the same electric motor of memory MEMO.

Reference is now made more particularly to FIGS. 5 and 7, detailed side views of a single disc cartridge of the present invention when located outside of receptacle 201 and in place in the receptacle, respectively. Cartridge CART₁ includes elastically deformable plastic exterior shell ENV₁. Shell ENV₁ includes top wall 207 that extends between side walls 202 and 203. When cartridge CART₁ is outside receptacle 201 top wall 207 has a concave configuration, with a nadir approximately on axis Ax_(r). When cartridge CART₁ is in receptacle 201, the outer edges of top face 207 are deflected downwardly so that the top face is substantially planar, as illustrated in FIG. 7. Extending inwardly from side walls 202 and 203 are flanges 204 and 205, having upper faces abutting against a lower face of hub MOY₁ when cartridge CART₁ is outside of receptacle 201. When cartridge CART₁ is in place in receptacle 201, side walls 202 and 203 are deflected downwardly so that the upper faces of flanges 204 and 205 are spaced from the lower face of hub MOY₁. When cartridge CART₁ is outside of receptacle 201 the spring force of top face 207 against hub MOY₁ provides a relatively secure static friction fit between flanges 214 and 215 and the bottom face of hub MOY₁ to seal the interior of shell ENV₁ from the outside environment. Downward deflection of side walls 202 and 203 when cartridge CART₁ is in receptacle 201 removes this sealing relationship and enables hub MOY₁ to turn freely in response to rotation of drive platter PLENM₁ about axis Ax_(r).

Downwardly depending from the bottom face of hub MOY₁ is circular flange MCPRE₁, concentric with hub axis Ax_(d). The outer face of flange MCPRE₁ is removed from Ax_(d) by a distance slightly less than the distance separating the inner wall of flange A₁ from axis Ax_(r). The outer wall of flange MCPRE₁ and the inner wall of lip A₁ are thus positioned with respect to each other so that in response to substantial misalignment between axis Ax_(r) of platter PLENM₁ and axis Ax_(d) of hub MOY₁ when cartridge CART₁ is in receptacle 201 a portion of the walls of the lip and flange engage each other. When cartridge CART₁ is approximately correctly positioned in receptacle 201 so that there is substantial alignment between axes Ax_(r) and Ax_(d), there is no contact between the adjacent walls of lip A₁ and flange MCPRE₁ and a bottom edge of the flange engages reference plane π of platter PLENM₁. Thereby, flange MCPRE₁ and wall A₁ can be considered as a "precentering means or mechanism" for cartridge CART₁.

Fixedly secured to hub MOY₁ is elastically deformable ring ROND₁, forming an elastically deformable mechanism for precisely centering hub MOY₁ relative to rotation axis Ax_(r) of platter PLENM₁. Ring ROND₁ includes a first surface 221 generally at right angles to the hub axis of rotation Ax_(d) and a second surface 222 extending generally coaxially with the hub axis of rotation. When cartridge CART₁ is inserted into receptacle 201, the elastic structure of ring ROND₁ is deformed so that surfaces 221 and 222 respectively bear against reference plane π and an interior wall of circular flange A₂, extending at right angles from reference plane π. The contact between surface 221 and plane π and surface 222 and the interior wall of flange A₂ frictionally holds ring ROND₁ in place against plane π and flange A₂ to repeatedly position hub axis Ax_(d) at the same location relative to rotation axis Ax_(r).

Shell ENV₁ and hub MOY₁ include a mechanism MTF₁ to transmit a compressive force F_(v) along hub axis Ax_(d), at right angles to the plane of disc DISC₁, to hub MOY₁ and ring ROND₁ when cartridge CART₁ is in receptacle 201. Mechanism MTF₁ includes a pad secured to top wall 207 and a ball captured against the pad. When cartridge CART₁ is outside of receptacle 201, as illustrated in FIG. 5, mechanism MTF₁ exerts virtually no force against hub MOY₁ whereby ring ROND₁ remains in a relatively relaxed, undeformed state because of the undeformed, concave state of top wall 207 and the positioning of side walls 202 and 203 which causes the top face of flanges 214 and 215 to engage the bottom face of disc 18. When cartridge CART₁ is in receptacle 201, top wall 207 is deflected downwardly whereby mechanism MTF₁ exerts a compressive force on hub MOY₁ along the hub axis Ax_(d). The compressional force along hub axis Ax_(d) causes ring ROND₁ to be deformed so that surfaces 221 and 222 thereof respectively engage plane π and the interior wall of flange A₂.

When cartridge CART₁ is inserted into receptacle 201, grooves RAIN₁ and RAIN₂ of the cartridge slide along and are guided on longitudinal tracks RL₁ and RL₂. Cartridge CART₁ is locked in receptacle 201 in response to a conventional lever (not shown) which is a part of memory MEMO and therefore external to the cartridge. The lever is an integral part of a threaded sleeve, a part of frame BAT₁ of memory MEMO. In response to the lever locking cartridge CART₁ in receptacle 201, top wall 207 is deflected from the concave position illustrated in FIG. 5 to the relatively flat position illustrated in FIG. 7. Simultaneously, side walls 202 and 203 descend vertically from the position illustrated in FIG. 5 to the position illustrated in FIG. 7; a typical downward movement of walls 202 and 203 is on the order of four millimeters. Hub MOY₁ is precentered inside of lip A₁. Precentering hub MOY₁ enables cartridge CART₁ to attain a proper position with relative ease when the cartridge is positioned in receptacle 201. As described supra, flange MCPRE₁ is positioned inside of lip A₁, with the bottom edge of the flange engaging reference plane π.

Hub MOY₁ is then precisely centered using ring ROND₁. The precise centering occurs in response to a sleeve (not shown) inside of frame BAT₁ causing a uniform pressure P_(v) to be exerted downwardly against ear 225 which extends outwardly from side walls 202 and 203 about the periphery of shell ENV₁. The uniform pressure P_(v) causes deformation of elastic shell ENV₁ from the position illustrated in FIG. 5 to the position illustrated in FIG. 7. By deforming shell ENV₁ to the position illustrated in FIG. 7, pressure P_(v) transmits a compressive stress to ring ROND₁ via mechanism MTF₁ and hub MOY₁. In response to the compressive stress applied to ring ROND₁, the ring is deformed. Prior to deformation, while force Fv is not applied, the diameter of ring ROND₁ is such that there is play of about 20 to 25 microns between surface 222 of the ring and the interior wall of flange A₂. In response to compressive force F_(v), the diameter of ring ROND₁ expands slightly so that the periphery of the ring, i.e., surface 222, contacts the inside walls of flange A₂ and exerts a lateral pressure P₁ perpendicular to the interior wall of flange A₂. In addition, the compressive force F_(v) on ring ROND₁ flattens the ring so that surface 221 of the ring contacts reference plane π, to exert a pressure P_(N) normal to the reference plane. Simultaneously with surface 221 of ring ROND₁ exerting a force against reference plane π, the bottom edge of flange MCPRE₁ exerts an additional normal pressure on reference plane π. Thus, the effect of compressive force F_(v) is to insure consistent centering of axis Ax_(d) of hub MOY₁, and therefore of the center of disc DISC₁, relative to axis Ax_(r). In addition, compressive force F_(v) provides an effective coupling between hub MOY₁ and platter PLENM₁. The coupling is provided by the static frictional force which effectively adheres flange A₁ to reference plane π and which effectively adheres surface 222 of ring ROND₁ to the wall of flange A₂.

Simultaneously with deformation of ring ROND₁ , flange 215 disengages from disc 218, as described supra. At this time, aperture FE_(c) opens to allow heads TEL₁ and TEL₂ to extend through wall 206 into shell CART₁ in proximity to opposite faces of disc DISC₁. With heads TEL₁ and TEL₂ in place, disc DISC₁ is rotatably driven by the connection between platter PLENM₁ and hub MOY₁, on which disc DISC₁ is fixedly mounted.

Additional details of the precentering and centering mechanism and the operation thereof are provided in copending, commonly assigned, simultaneously filed application entitled "Magnetic Disc Cartridge With Centering Structure", U.S. Ser. No. 462,911, filed Feb. 1, 1983.

The ventilation system according to the present invention is applicable to a cartridge containing plural removable magnetic discs, as illustrated in connection with cartridge CART₂, FIG. 6, containing discs DISC₂ -DISC₅. The principles of assembly and operation of cartridge CART₂ are identical to those of cartridge CART₁. Cartridge CART₂ includes hub MOY₂ on which are mounted discs DISC₂ -DISC₅. Hub MOY₂ carries elastically deformable, precision centering disc ROND₂, responsive to forces exerted through mechanism MTF₂, including a pad and ball. Hub MOY₂ is roughly centered by a precentering mechanism similar to that described in connection with FIGS. 5 and 7; in particular, hub MOY₂ includes circular flange MCPRE₂, similar to flange MCPRE₁.

Consideration is now given to the ventilation system adapted to be used in connection with the single disc cartridge CART₁ of FIGS. 5 and 7, by referring to FIG. 8. The ventilation system supplies gas, preferably air, to opposite faces of disc DISC₁, to lift off particulate materials having a tendency to become attached to the disc data containing portion while the disc is not in use and to supply a flow of gas over the disc data containing portion while the disc is rotating about axis Ax_(d) in receptacle 201, to substantially prevent particulate material from adhering to the portion while the disc is rotating. To these ends, cartridge CART₁ includes conduits COND₁ and COND₂ which extend generally radially of disc DISC₁. Air is pumped to ends of conduits COND₁ and COND₂ beyond the periphery of disc CART₁ by way of filter FILT₃, contained in cartridge CART₁. Air supplied to conduits COND₁ and COND₂ is directed against opposite faces of disc DISC₁ by orifices TR₁ -TR₆ and TR₇ -TR₁₂ on conduits COND₁ and COND₂, respectively.

Orifices TR₁ -TR₆ and TR₇ and TR₁₂ are positioned on a side wall of conduits COND₁ and COND₂ so that air jets flowing through the apertures flow in the same direction as the rotation direction of disc DISC₁. The air flowing through the orifices of conduits COND₁ and COND₂ flows outwardly away from axis Ax_(d) with a spiral motion past heads TEL₁ and TEL₂ through orifice PAST₁ on smooth substantially circular interior wall 525 of cartridge CART₁, which interior wall surrounds and is closely spaced from disc DISC₁ Aperture PEVC₁ is positioned between conduits COND₁ and COND₂ and heads TEL₁ and TEL₂ when cartridge CART₁ is in receptacle 201. Conduits COND₁ and COND₂ and aperture PEVC₁ are positioned such that the vast majority of the air flowing between them makes at least one spiral turn. Heads TEL₁ and TEL₂ are positioned relative to the orifices in conduits COND₁ and COND₂ and orifice PEVC₁ such that there is laminar air flow past the heads, whereby the air flow does not affect the position of the heads relative to disc DISC₁. In particular, the laminar air flow does not cause the spacing between heads TEL₁ and TEL₂ relative to disc DISC₁ to change so that signals derived from data tracks on disc DISC₁ are not affected by the air flowing between conduits COND₁ and COND₂ and orifice PEVC₁. To these ends, there is more than a 180° separation between heads TEL₁ and TEL₂ and conduits COND₁ and COND₂, as well as orifice PEVC₁. The smoothness of wall 525 also contributes to the laminar flow past heads TEL₁ and TEL₂, as does introducing air through the orifices of conduits COND₁ and COND₂ in the same direction as the rotation of disc DISC₁.

Air flowing through orifice PEVC₁ flows into conduit CEVC₁. Conduit CEVC₁ is an integral part of cartridge CART₁, being located behind interior wall 525 of the cartridge in which orifice PEVC₁ is located. Conduit CEVC₁ has a longitudinal axis generally parallel to the axis of rotation Ax_(d) of disc DISC₁. Air flowing through conduit CEVC₁ flows into conduit 512, thence through conduit CEVM₁ into filter FILT₁. Conduits 512, CEVM₁ and filter FILT₁ are located in frame BAT₁ of disc memory unit MEMO. Conduit 512 is aligned with conduit CEVC₁ when cartridge CART₁ is inserted in receptacle TR₁. Conduit CEVM₁ includes an opening responsive to air flowing through conduit 512, whereby conduit CEVM₁ directs air radially of axis Ax_(d) of disc DISC₁. Filter FILT₁ has a cylindrical configuration, with an axis coincident with axis Ax_(r) of rotary platter PLENM₁.

Air is pumped longitudinally through filter FILT₁ by fan TURB₁, having radially directed blades 513. Fan TURB₁ and disc platter PLENM₁ are driven by the same motor at the same speed. Air pumped by fan TURB₁ is confined to a relatively narrow region between blades 513, by virtue of close spacing between pie shaped troughs 514 between the blades and a roof immediately above the blades. Thereby, as illustrated in FIG. 13, air from filter FILT₁ flows radially between blades 513 and is carried between the blades to orifice 515, positioned in circular wall 1516 slightly beyond the periphery of fan TURB₁. The air flowing through orifice 515 flows longitudinally through cylindrical filter FILT₂, thence to cylindrical filter FILT₃. Filters FILT₃ and FILT₂ have aligned longitudinal axes when cartridge CART₁ is in receptacle 201. While filters FILT₂ and FILT₃ are schematically shown in FIG. 8 as cylinders, they preferably have a generally triangular cross-section, as illustrated in FIGS. 9 and 11.

The air filtered by filter FILT₃ is introduced through the apertures in conduits COND₁ and COND₂ at sufficient pressure to form decontaminating air jets that lift dust particles that become attached to the surface of disc DISC₁ during periods while cartridge CART₁ is not in use. The air jets are supplied against the opposite faces of disc DISC₁, around the center of the disc. The air jets are driven by centrifugal force produced in response to rotation of the disc, toward the periphery of the disc, where they flow through exhaust orifice PEVC₁. The speed of the air flowing over the faces of disc DISC₁ is augmented by the partial vacuum created in the center of drive platter PLENM₁ by fan TURB₁. Thus, air is circulated through the ventilation system in response to rotation of disc DISC₁ which causes the air to circulate tangentially on the surfaces of each side of the disc at a speed equal to the disc rotation speed, and by fan TURB₁ which aspirates air which passes through orifice PEVC₁ and conduits CEVC₁, 512, CEVM₁, as well as filters FILT₁, FILT₂ and FILT₃. Pump TURB₁ also draws fresh air through filter FILT₁.

To minimize the amount of contaminated air introduced into cartridge CART₁ while it is in receptacle 201 and to enhance the efficiency of the ventilating system, heads TEL₁ and TEL₂ are located in hermetically sealed enclosure EP, FIG. 12, of disc memory unit MEMO. Thereby, when a gate for opening FE_(c) is opened when cartridge CART₁ is inserted in receptacle A₂, no contaminated air is introduced through the opening as heads TEL₁ and TEL₂ are urged in proximity with disc DISC₁.

Filter FILT₂ removes substantially all contaminates produced by bearings of drive platter PLENM₁ and an electric motor that drives the drive platter. Filter FILT₁ is the main filter for eliminating dust particles that have been lifted off of disc DISC₁ by air introduced through conduits COND₁ and COND₂, as well as contaminates removed from the walls of conduits CEVC₁, 512 and CEVM₁ by the air flowing against these walls. Filter FILT₃ substantially eliminates particulate materials produced at the interface between cartridge CART₁ and the wall of receptacle 201 of disc memory unit MEMO.

Reference is now made to FIGS. 9-11, detailed drawings of the portion of the ventilation system located inside of cartridge CART₁ Shell ENV₁ of cartridge CART₁ is formed of an upper part ENVH₁, intermediate part ENVM₁ and lower part ENVB₁. Orifice PEVC₁, included in intermediate part ENVM₁, is selectively closed by air exhaust gate PECH₁. Gate PECH₁ is mechanically connected to head access gate PAT₁ which selectively closes opening FE_(c) when cartridge CART₁ is not in place in receptacle 201. Gate PECH₁ closes conduit CEVC₁ when cartridge CART₁ is not in receptacle 201. Similarly, gate ENVM₁ closes conduits COND₁ and COND₂ when cartridge CART₁ is not in receptacle 201.

As illustrated in FIG. 10, gates PECH₁, PAT₁ and PADM₁ extend upwardly from lower cartridge segment ENVB₁ into cartridge segment ENVM₁. The height of gates PECH₁, PAT₁ and PADM₁ is such that the upper edges of the gates abut against the bottom face of upper cartridge segment ENVH₁ to provide the desired sealing or closing effect when cartridge CART₁ is not in receptacle 201. Gates PECH₁ and ENVM₁ slide on rubberized joints on cartridge segment ENVB₁ between the open and closed positions thereof by a motion that is generally radial with respect to the axis of disc DISC₁, while gate PAT₁ slides peripherally relative to the disc on another rubberized joint. To provide simultaneous opening and closing of gates PECH₁ and PST₁, actuating mechanisms for the gates are connected together by metallic band RUB₁, having one end connected to an edge of gate PAT₁, and a second edge connected to one face of plate 515. Band RUB₁ is held in position about the periphery of disc DISC₁, between gate PAT₁ and plate 535 by posts 536. The face of plate 535 opposite from the face connected to band RUB₁ is connected to one end of compression spring SP₁, and to one end of metal band LAM₁. The other ends of spring SP₁ and band LAM₁ are respectively connected to an interior wall of cartridge CART₁ and to a face of gate PECH₁. With gates PECH₁ and PAT₁ in the closed position, as illustrated in FIG. 11, spring SP₁ is compressed, to draw plate 515 toward the wall of cartridge CART₁ on which spring SP₁ is mounted. Thereby, gate PECH₁ is urged in position, to block a passageway in intermediate section ENVM₁ between conduit CEVC₁ and orifice PEVC₁. Simultaneously, plate 515 tensions band RUB₁, to pull gate PAT₁ over aperture or opening FE_(c).

When cartridge CART₁ is inserted in place in receptacle 201, a sleeve (not shown) which is an integral part of frame BAT₁ causes gate PAT₁ to move peripherally from the position shown in FIG. 11 to the position shown in FIG. 9. The action of the sleeve on gate PAT₁ causes the gate to tension band RUB₁, to drive plate 535 from the position illustrated in FIG. 11 to the position illustrated in FIG. 9, whereby spring SP₁ expands. The movement of plate 535 from the position illustrated in FIG. 11 to the position illustrated in FIG. 9, causes band LAM₁ to translate gate PECH₁ from the position illustrated in FIG. 11 to the position illustrated in FIG. 9. Thereby, orifice PEVC₁ is open, to enable air circulating inside of cartridge CART₁ to flow into conduit CEVC₁.

Simultaneously with opening of gates PECH₁, gate PADM₁ is open. To this end, one face of gate PADM₁ is connected to one end of torsion spring SP₂, having a second end fixedly connected to lower cartridge segment ENVB₁. Gate PADM₁ includes a downwardly depending tab that engages opposed walls in aperture 516 in lower segment ENVB₁ when the gate is opened and closed. Aperture 516 leads to a conduit in frame BAT₁, which conduit is filled by filter FILT₂.

As illustrated in FIG. 11, when cartridge CART₁ is not in receptacle 201, aperture 516 is not in fluid flow relationship with filter FILT₃ by virture of gate PADM₁ being closed. To open gate PADM₁, the sleeve which acts on gate PAT₁ acts on gate PADM₁ to overcome the bias of torsion spring SP₂, and urge gate PADM₁ against the back edge of aperture 516. Thereby, air flows through aperture 516 and filter FILT₃ into conduits COND₁ and COND₂, thence through the orifices of the conduits against opposite faces of disc DISC₁. As illustrated in FIG. 9, the air flowing through the orifices of conduits COND₁ and COND₂ flows in an outwardly directed spiral at least once around disc DISC₁, thence through orifice PEVC₁ into conduit CEVC₁.

Immediately after gate PAT₁ opens aperture FE_(c), heads TEL₁ and TEL₂ move through the aperture to a designated track in the data portion of disc DISC₁, as illustrated in FIG. 9 for head TEL₁. To these ends, head TEL₁ is mounted at the end of support arm BS₁, having another end fixedly mounted on one end of leg POS₁, another end of which is fixedly connected to shaft 517. Shaft 517 is rotatably driven by a motor (not shown) to drive head TEL₁ from a position outside of cartridge CART₁ to a position over an addressed track on disc DISC₁.

Shaft 517, leg POS₁, arm BS₁ and head TEL₁ are located in hermetically sealed enclosure EP, FIG. 12. Enclosure EP is progressively pressurized in response to rotation of disc DISC₁ being initiated. Thereby, there is a minimum amount of turbulence in the air exchanged between enclosure EP and the interior of cartridge CART₁ to maintain the position of heads TEL₁ and TEL₂ constant relative to disc DISC₁. The introduction of turbulent air in the vicinity of heads TEL₁ and TEL₂ by virtue of a sudden pressure change across opening FE_(c) could possibly damage the heads, by causing them to deflect downwardly into contact with disc DISC₁.

Reference is now made to FIG. 12 of the drawing, a cross-sectional view of the ventilation system in memory unit MEMO with cartridge CART₁ being located inside of receptacle 201. The memory unit of FIG. 12 includes disc DISCNA₁, permanently mounted in the memory unit coaxially with disc DISC₁ so that both discs are driven by rotary platter PLENM₁ when cartridge CART₁ is in receptacle 201. While disc DISC₁ and DISCNA₁ are being driven, data are written onto and read from them by heads TEL₁ -TEL₄, which are located in sealed enclosure EP when the discs are not being driven. Heads TEL₃ and TEL₄ are driven from enclosure EP into proximity with discs DISC₁ and DISCNA₁ in the same manner and by a similar mechanism to that described supra to drive heads TEL₁ and TEL₂ into proximity with disc DISC₁ of cartridge CART₁.

With cartridge CART₁ in place in receptacle 201, axis Ax_(d) of disc DISC₁ is precentered by flanges A₁ and MCPRE₁, respectively carried by rotary platter PLENM₁ of disc memory unit MEMO and hub MOY₁ of cartridge CART₁. After the axis of disc DISC₁ has been precentered, the disc axis is precisely centered by ring ROND₁ engaging reference plane π and flange A₂ in response to a compressive force being exerted on compressive stress transmission mechanism MTF₁.

On FIG. 12, the flow path through filter FILT₁ to troughs 514 between vanes 513 of fan TURB₁, mounted coaxially with axis Ax_(r), is clearly indicated. Blades or vanes 513 have a height relative to trough 514 and wall 519 to cause the air flowing from filter FILT₁ to be captured between adjacent ones of the vanes so that the air flows in a generally spiral path, as indicated in FIG. 13, to filter FILT₂. From filter FILT₂ the air flows into filter FILT₃ to conduits COND₁ and COND₂. In addition, air flows from filter FILT₂ through orifice 520 into conduits COND₃ and COND₄. Conduits COND₃ and COND₄ contain orifices similar to the orifices in conduits COND₁ and COND₂ to supply high pressure air against opposite faces of disc DISCNA₁. The air directed against the opposite faces of disc DISCNA₁ circulates in an outwardly directed spiral to an orifice positioned similarly to orifice PEVC₁. The air circulated in the chamber including disc DISCNA₁ flows into conduit 512, thence conduit CEVM₁ and back to filter FILT₁.

Rotary drive platter PLENM₁ for discs DISC₁ and DISCNA₁ and fan TURB₁ is driven about axis Ax_(r) by motor MOT₁. Motor MOT₁ includes a stator containing laminated cores 521 which extend radially from axis Ax_(r). Coils 522 are wound on cores 521 and are excited in a conventional manner to drive platter PLENM₁. Fan TURB₁ is mounted on platter PLENM₁ coaxially with axis Ax_(r) so that the fan is turned at the same speed as discs DISC₁ and DISCNA₁. Cores 521 are fixedly positioned in frame BAT₁ immediately below fan TURB₁.

Drive platter PLENM₁ includes ball bearings 523 for supporting flange A₂, and therefore the drive mechanism in cartridge CART₁ for disc DISC₁. In addition, ball bearings 524 are provided between motor MOT₁ and fan TURB₁ and therefore the drives for disc DISC₁ and DISCNA₁. Ball bearings 523 and 524 have a tendency to emit oil and other contaminating particulate materials. To prevent the particualte materials from ball bearings 523 and 524 from contaminating the space in cartridge CART₁ where disc DISC₁ is located, a tortuous path including baffles CHIC₁ is provided along the top wall of shell ENV₁ between the center portion of the cartridge, inside of the inner diameter of disc DISC₁, into the region where the data containing portion of the disc is located. Baffles CHIC₁ may be replaced with ferrofluidic joints, such as those manufactured by Ferrofluidics Incorporated.

Reference is now made to FIG. 14 of the drawing, a side sectional view of an embodiment of the drawing including four rotatable discs DISC₂ -DISC₅, carried by hub MOY₂, in turn driven by drive platter PLENM₂, integral with motor MOT₂. All of discs DISC₂ -DISC₅ are included in cartride CART₂.

Opposite faces of discs DISC₂ -DISC₅ are ventilated by air supplied to them by conduits COND₅ -COND₁₂, mounted similarly to conduits COND₁ and COND₂. Conduits COND₅ -COND₁₂ are supplied with air flowing through filter FILT₆, in turn responsive to air flowing through filter FILT₅. Filter FILT₆ and conduits COND₅ -COND₁₂ are an integral part of cartridge CART₂, while filter FILT₅ is a part of frame BAT₁ of memory unit MEMO. Air is supplied to filter FILT₅ by a structure integral with frame BAT₁, which structure comprises fan TURB₂ and filter FILT₄. Fan TURB₂ is driven by motor MOT₂, mounted coaxially with the axis of rotation of drive platter PLENM₂.

Air from conduits COND₅ -COND₁₂ has a tendency to be entrained adjacent the surface of the disc to which the air is initially directed. Air directed against each of the surfaces of discs DISC₂ -DISC₅ flows in an outwardly directed spiral to an orifice (not shown) associated with each of the discs, which orifice is similar to orifice PEVC₁, FIGS. 9 and 11. The air flow patterns in the multi-disc cartridge and the apparatus driving the multi-disc cartridge are thereby very similar to the air flow pattern in the single disc cartridge and the drive mechanism therefor, as described supra.

Data are written into and read from opposite faces of discs DISC₂ -DISC₅ by heads TEL₅ -TEL₁₂. Heads TEL₅ -TEL₁₂ are located in a hermetically sealed enclosure when cartridge CART₂ is not in place in receptacle 201, in a manner similar to that described in connection with FIG. 12. To prevent particulate material, particularly in the form of oil from bearings included in the structure of FIG. 14, from reaching the data containing portion of discs DISC₂ -DISC₅, a tortuous path is provided between the interior of cartridge CART₂, adjacent the axis of rotation of the disc, and the portion of the discs where data are located. The tortuous path comprises a baffle depending downwardly from the top interior wall of cartridge CART₂.

While there have been described and illustrated several specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims. For example, fan mechanisms TURB₁ and TURB₂ may be installed on hubs MOY₁ and MOY₂ inside of cartridges CART₁ and CART₂, respectively. 

I claim:
 1. In combination, a magnetic disc cartridge having a disc including a rotation axis; a housing for the cartridge, the housing including: transducer head means positioned above a portion of the magnetic disc where data are recorded when the cartridge is in the housing, a platter having a rotation axis coincident with the disc rotation axis when the cartridge is in the housing; a recirculating gas flow path extending from the housing into the cartridge past the heads, thence out of the cartridge and back to the housing; the gas flow path including a first filter in the housing, the flow path through the first filter being coaxial with the disc rotation axis into a plenum in the housing, the plenum including a plate having a rotation axis coincident with the disc axis, the disc when rotated about the axis thereof inducing an outwardly directed gas flow from the first filter into a first passage, the first passage being at a radial position beyond the edges of the platter and disc, the first passage being aligned with a second passage in the cartridge when the cartridge is in the housing so gas flowing into the first pasasge flows into the second passage, filter means in at least one of said passages, the gas flow path in the cartridge including: means for feeding gas flowing through the second passage to the portion of the disc where data are recorded and an orifice positioned beyond the edge of the disc, the gas feeding means and the orifice being positioned so that gas flows out of the second passage in a spiral path past the head means, thence to the orifice, and a first conduit through which the gas flowing into the orifice flows; the gas flow path in the housing including a second conduit positioned to receive gas flowing in the first conduit and for supplying the gas flowing in the first conduit to the first filter when the cartridge is in the housing.
 2. The combination of claim 1 wherein the filter means includes separate second and third filters respectively positioned in the first and second conduits, the first filter being positioned to intercept dust particles lifted off of the disc by the gas flowing out of the means for feeding, the second filter being positioned to intercept contaminates introduced into the recirculation path by bearings on the rotating platter, the third filter being positioned to intercept particles introduced into the recirculating path at abutting surfaces of the cartridge and housing.
 3. The combination of claim 1 wherein the platter includes radially extending vanes and a central aperture through which gas from the first filter flows, the gas flowing through the central aperture being directed by the vanes into an outwardly directed spiral, thence to the first conduit.
 4. The combination of claim 1 wherein the cartridge includes gate means for enabling the head means to be inserted therein from the housing, and means for maintaining the gate means in a closed position except while the cartridge is in situ in the housing.
 5. The combination of claim 1 wherein the means for supplying includes a passage extending radially with respect to the disc axis and having plural gas supplying orifices at different radii with respect to the disc axis.
 6. The combination of claim 5 wherein the plural orifices of the radially extending passage are positioned to direct the gas in the same direction as the disc is turning.
 7. The combination of claim 6 wherein the plural orifices on the radially extending passages, the orifice positioned beyond the disc edge, and the head means are positioned so there is laminar flow of the gas past the head.
 8. The combination of claim 6 wherein the plural orifices on the radially extending passage, the orifice positioned beyond the disc edge, and the head means are positioned so the gas flow in the spiral is through about 360° and the gas flow from the plural orifices on the radially extending passage to the head is about one-half of the arcuate distance of the gas flow from the plural orifices to the orifice positioned beyond the disc edge.
 9. Apparatus for ventilating a magnetic disc, the disc having a surface portion containing data, the apparatus keeping the surface-portion substantially free of particulate materials, comprising an enclosure in which the disc is mounted for rotation about an axis, means for establishing a recirculating gas path, said path including: means for supplying gas jets completely across the portion as the disc is rotating to prevent particulate material from adhering to the disc portion, an orifice for removing gas from the enclosure, and fan means for circulating the gas removed from the enclosure by the orifice about the axis as the disc is rotating and for supplying the circulated gas back to the gas jets supplying means, the disc being part of a memory unit having magnetic head means for transducing data from the portion, the enclosure including the head means being positioned relative to the orifice and inlet means for the gas jet supplying means such that the gas has laminar flow as the gas passes the magnetic head means, the laminar gas flow being such that it does not affect the position of the head means relative to the disc portion, the recirculating path including filter means for removing particulate materials from the gas circulating in the recirculating path between the orifice and the aperture means, the inlet means including aperture means disposed at different radial positions across the disc above the portion, and the orifice being positioned farther from the axis than any part of the aperture means, the orifice being positioned relative to the aperture means so that the gas flows in a spiral through approximately at least one complete revolution from the aperture means to the orifice.
 10. The apparatus of claim 9 further including means for blocking the recirculating path while the enclosure is removed from a receptacle of the disc memory unit containing the head means.
 11. The apparatus of claim 10 wherein the blocking means includes first gate means between an outlet of the fan means and the aperture means and second gate means between an inlet of the fan means and the orifice.
 12. The apparatus of claim 10 wherein the filter means includes separate first and second filters in the inlet and outlet of the fan means. 